Download 3/3/2015 An Overview of Animal Diversity 1. General Features of Animals Chapter 32:

3/3/2015
Chapter 32:
An Overview of Animal Diversity
1. General Features of Animals
2. The History of Animals
1. General Features of Animals
General Characteristics of Animals
•
•
animals are multicellular eukaryotic heterotrophs that ingest
their food and digest it internally
animals have tissues that develop from embryonic germ layers
•
•
tissues are groups of similar cells that act as a
functional unit
nerve & muscle
tissue are derived
characters of
animals
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Animal Cell Structure & Specialization
Animal cells lack
cell walls and can
adopt a wide
variety of specific
cell fates (e.g.,
muscle, nerve,
kidney, liver cells)
Animal Body Plans
Almost all animal species have
symmetrical body plans:
•
some animal groups are
characterized by body plans
with radial symmetry
•
most animal groups exhibit
bilateral symmetry
Radial symmetry
Animal body plans are dependent on
the Hox genes, a set of genes unique
to the Animal Kingdom.
Bilateral symmetry
Animal Reproduction & Development
Most animals reproduce sexually with
the diploid phase of the life cycle
being dominant.
Following fertilization, early animal
development unfolds in the
characteristic stages shown here.
CLEAVAGE – rapid cell division
without cell growth
GASTRULATION – reorganization of
cells to produce the germ layers
Zygote
Cleavage
Eight-cell
stage
Cleavage
Blastula
Blastocoel
Cross section
of blastula
Gastrulation
Cross section
of gastrula
Blastopore
Blastocoel
Endoderm
Ectoderm
Archenteron
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The Germ Layers
Through the process of gastrulation, 2 or 3 germ layers are produced
from which the overall body plan and all body structures develop.
• species that are diploblastic have only
2 germ layers – ectoderm and endoderm
• triploblastic species produce all 3 germ layers
ECTODERM – outermost germ
layer that gives rise to the nervous
system and external structures
ENDODERM – innermost germ
layer that gives rise to the
digestive structures
MESODERM – middle germ layer
that gives rise to structures not
derived from ectoderm or endoderm
Body Cavities
Most triploblastic animal species have body cavity separate from the
gut called a coelom associated with mesodermal tissues.
(a) Coelomate
Coelom
•
Body covering
(from ectoderm)
coelomates have a
coelom completely
surrounded by
mesodermal tissue
Tissue layer
lining coelom
and suspending
internal organs
(from mesoderm)
Digestive tract
(from endoderm)
Key
Ectoderm
Endoderm
Mesoderm
(b) Pseudocoelomate
Body covering
(from ectoderm)
Pseudocoelom
•
Muscle layer
(from
mesoderm)
pseudocoelomates have a
coelom bordered on the
interior by endoderm
Digestive tract
(from endoderm)
Key
Ectoderm
Mesoderm
Endoderm
(c) Acoelomate
Body covering
(from ectoderm)
•
acoelomates are
triploblastic animals
do not have a coelom
Tissuefilled region
(from
mesoderm)
Wall of digestive cavity
(from endoderm)
Key
Ectoderm
Mesoderm
Endoderm
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Protostome vs
Deuterostome
Development
(a) Cleavage
Deuterostome development
(examples: echinoderms,
chordates)
Eight-cell stage
Protostome development
(examples: molluscs,
annelids)
Eight-cell stage
Radial and indeterminate
Spiral and determinate
•
•
in PROSTOSTOMES, the
blastopore becomes
the mouth, cleavage is
spiral & determinate
Coelom
(b) Coelom
formation
Archenteron
Coelom
Mesoderm
Blastopore
Blastopore
Solid masses of mesoderm
split and form coelom.
in DEUTEROSTOMES,
the blastopore becomes
the anus (a second
opening becomes the
mouth), cleavage is
radial & indeterminate
(c) Fate of the
blastopore
Mesoderm
Folds of archenteron
form coelom.
Mouth
Anus
Digestive tube
Key
Ectoderm
Mesoderm
Endoderm
Mouth
Mouth develops from blastopore.
Anus
Anus develops from blastopore.
2. The History of Animals
Phylogeny of the Animal Kingdom
Metazoa
Porifera
(basal animals)
Eumetazoa
Ctenophora
Cnidaria
Acoela (basal
bilaterians)
Deuterostomia
Bilateral
symmetry
Three germ
layers
Lophotrochozoa
Bilateria (most animals)
True
tissues
Ecdysozoa
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Steps in the Origin of Multicellular Animals
Protists called
choanoflagellates
are the closest living
relatives to animals.
Individual
choanoflagellate
Choanoflagellates
OTHER
EUKARYOTES
Sponges
Animals
Collar cell
(choanocyte)
Other
animals
Cell-Cell Adhesion & Multicellularity in Animals
Genes involved in cell-cell adherence such as cadherin that
are unique to animals were key to multicellularity.
Choanoflagellate
Hydra
“CCD” domain (only
found in animals)
Fruit
fly
Mouse
History of Animals Spans Over 500 Million Years
Origin and
diversification
of dinosaurs
535−525 mya:
Cambrian explosion
560 mya:
Ediacaran animals
Era
Neoproterozoic
1,000
365 mya:
Early land
animals
Cenozoic
Mesozoic
Paleozoic
542
Diversification
of mammals
251
65.5
0
Millions of years ago (mya)
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The Proterozoic Era (1 billion to 542 mya)
Ediacaran animals were largely
sessile and are some of the earliest
animals in the fossil record.
1.5 cm
0.4 cm
Bore hole
(a) Mawsonites spriggi
(b) Spriggina floundersi
0.1 mm
The Paleozoic Era (542 to 251 mya)
The Cambrian explosion (535 to 525 mya) refers to a period when the
ancestors of most major animal groups first appear in the fossil record.
•
most have bilateral symmetry and complete “one way” digestive tracts
•
hypothesized to be due to increased O2 and evolution of the Hox genes
1 cm
Hallucigenia
fossil (530 mya)
The Transition to Land
375 million year old fossils of Tiktaalik roseae are the earliest
evidence of the vertebrate transition from water to land.
•
has characteristics of
both fish & amphibians
Tiktaalik roseae
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Mesozoic Era (251 to 65.5 mya)
Dinosaurs were the dominant land vertebrates.
• the first mammals in
the fossil record
• the first evidence of
coral reef ecosystems
• end of this era coincides
with an asteroid impact
and mass extinctions
Cenozoic Era (65.5 mya to present)
• mammals
increased in size
and variety to
occupy niches
vacated by mass
extinction and
become the
dominant land
vertebrates
Porifera
Ctenophora
Eumetazoa
Metazoa
ANCESTRAL
PROTIST
Cnidaria
Acoela
Hemichordata
Echinodermata
Chordata
Platyhelminthes
Lophotrochozoa
670 million
years ago
Deuterostomia
Bilateria
770 million
years ago
680 million
years ago
The
Diversification
of Animals
Rotifera
Ectoprocta
Brachiopoda
Mollusca
Ecdysozoa
Annelida
Nematoda
Arthropoda
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